Passive acoustic monitoring of the temporal variability of odontocete tonal sounds from a long-term marine observatory.

Lin TH, Yu HY, Chen CF, Chou LS - PLoS ONE (2015)

Bottom Line:
The seasonal variation of whistle usage involved the previous three parameters, in addition to the diversity of whistle clusters.Our results indicated that the species and behavioral composition of the local odontocete community may vary among seasonal and diurnal cycles.The current monitoring platform facilitates the evaluation of whistle usage based on group behavior and provides feature vectors for species and behavioral classification in future studies.

ABSTRACTThe developments of marine observatories and automatic sound detection algorithms have facilitated the long-term monitoring of multiple species of odontocetes. Although classification remains difficult, information on tonal sound in odontocetes (i.e., toothed whales, including dolphins and porpoises) can provide insights into the species composition and group behavior of these species. However, the approach to measure whistle contour parameters for detecting the variability of odontocete vocal behavior may be biased when the signal-to-noise ratio is low. Thus, methods for analyzing the whistle usage of an entire group are necessary. In this study, a local-max detector was used to detect burst pulses and representative frequencies of whistles within 4.5-48 kHz. Whistle contours were extracted and classified using an unsupervised method. Whistle characteristics and usage pattern were quantified based on the distribution of representative frequencies and the composition of whistle repertoires. Based on the one year recordings collected from the Marine Cable Hosted Observatory off northeastern Taiwan, odontocete burst pulses and whistles were primarily detected during the nighttime, especially after sunset. Whistle usage during the nighttime was more complex, and whistles with higher frequency were mainly detected during summer and fall. According to the multivariate analysis, the diurnal variation of whistle usage was primarily related to the change of mode frequency, diversity of representative frequency, and sequence complexity. The seasonal variation of whistle usage involved the previous three parameters, in addition to the diversity of whistle clusters. Our results indicated that the species and behavioral composition of the local odontocete community may vary among seasonal and diurnal cycles. The current monitoring platform facilitates the evaluation of whistle usage based on group behavior and provides feature vectors for species and behavioral classification in future studies.

Mentions:
In addition to the detected duration, the whistle usage of local odontocetes also varied among the seasonal and diurnal cycles (Fig 4). The mode frequencies tended to be lower in winter and spring. Higher mode frequencies could also be observed during the nighttime in winter, summer, and fall, compared with those during the daytime. The diversity indices of representative frequencies in the daytime were generally lower than in the nighttime. The differences were more obvious in winter and spring. For the diversity indices of whistle clusters, the diurnal variation was not as evident. However, the seasonal variation showed that the diversity indices of whistle clusters were higher in winter. The seasonal and diurnal changing patterns of sequence complexity were much more complicated. The entropic slopes tended to be lower in the daytime, but this phenomenon can be observed only during certain months. Permutational multivariate analysis of variance revealed that the whistle usage varied significantly between day and night periods (Pseudo-P < 0.001) and among four seasons (Pseudo-P < 0.001). Furthermore, the level of data dispersion changed significantly among diurnal (Pseudo-P < 0.001) and seasonal cycles (Pseudo-P < 0.001) based on the homogeneity test of multivariate dispersions.

Mentions:
In addition to the detected duration, the whistle usage of local odontocetes also varied among the seasonal and diurnal cycles (Fig 4). The mode frequencies tended to be lower in winter and spring. Higher mode frequencies could also be observed during the nighttime in winter, summer, and fall, compared with those during the daytime. The diversity indices of representative frequencies in the daytime were generally lower than in the nighttime. The differences were more obvious in winter and spring. For the diversity indices of whistle clusters, the diurnal variation was not as evident. However, the seasonal variation showed that the diversity indices of whistle clusters were higher in winter. The seasonal and diurnal changing patterns of sequence complexity were much more complicated. The entropic slopes tended to be lower in the daytime, but this phenomenon can be observed only during certain months. Permutational multivariate analysis of variance revealed that the whistle usage varied significantly between day and night periods (Pseudo-P < 0.001) and among four seasons (Pseudo-P < 0.001). Furthermore, the level of data dispersion changed significantly among diurnal (Pseudo-P < 0.001) and seasonal cycles (Pseudo-P < 0.001) based on the homogeneity test of multivariate dispersions.

Bottom Line:
The seasonal variation of whistle usage involved the previous three parameters, in addition to the diversity of whistle clusters.Our results indicated that the species and behavioral composition of the local odontocete community may vary among seasonal and diurnal cycles.The current monitoring platform facilitates the evaluation of whistle usage based on group behavior and provides feature vectors for species and behavioral classification in future studies.

ABSTRACTThe developments of marine observatories and automatic sound detection algorithms have facilitated the long-term monitoring of multiple species of odontocetes. Although classification remains difficult, information on tonal sound in odontocetes (i.e., toothed whales, including dolphins and porpoises) can provide insights into the species composition and group behavior of these species. However, the approach to measure whistle contour parameters for detecting the variability of odontocete vocal behavior may be biased when the signal-to-noise ratio is low. Thus, methods for analyzing the whistle usage of an entire group are necessary. In this study, a local-max detector was used to detect burst pulses and representative frequencies of whistles within 4.5-48 kHz. Whistle contours were extracted and classified using an unsupervised method. Whistle characteristics and usage pattern were quantified based on the distribution of representative frequencies and the composition of whistle repertoires. Based on the one year recordings collected from the Marine Cable Hosted Observatory off northeastern Taiwan, odontocete burst pulses and whistles were primarily detected during the nighttime, especially after sunset. Whistle usage during the nighttime was more complex, and whistles with higher frequency were mainly detected during summer and fall. According to the multivariate analysis, the diurnal variation of whistle usage was primarily related to the change of mode frequency, diversity of representative frequency, and sequence complexity. The seasonal variation of whistle usage involved the previous three parameters, in addition to the diversity of whistle clusters. Our results indicated that the species and behavioral composition of the local odontocete community may vary among seasonal and diurnal cycles. The current monitoring platform facilitates the evaluation of whistle usage based on group behavior and provides feature vectors for species and behavioral classification in future studies.